Various types of organosilanes and polyorganosiloxanes such as hydroxyl-endblocked polydimethylsiloxanes have been employed to surface treat the surfaces of particulate inorganic fillers, particularly reinforcing silica fillers, to render the surfaces of the fillers hydrophobic. As a result the handling properties of the uncured elastomer (filler-gum) composition are improved and the tendency for the composition to crepe harden is reduced. The physical properties such as tensile strength of the cured elastomers may also be improved.
For example, U.S. Pat. No. 2,954,357 (Fekete, issued Sept. 27, 1960) teaches the use of certain dihydrocarbon polysiloxane oils having a hydrocarbon substituent to silicon aton ratio of 1.6 to 2.0, preferably from 1.889 to 2.0 and an average of from 1 to 2 preferably from 1 to 1.5, lower alkoxy groups, per terminal silicon atom to improve the bin-aging characteristics of filler-containing polydiorganosiloxane gum compositions. Ethoxy radicals appear to be the alkoxy radical of choice and the polysiloxane oils used in these compositions contain at least 4 and as much as 35 or more dihydrocarbonsiloxy units per molecule and have molecular weights of from about 400 to 2700, preferably from about 600 to 1500. The method of preparing such polysiloxane oils is said to be taught in U.S. Pat. No. 2,909,549 (Bailey, issued Oct. 20, 1959) which teaches that alkoxy-endblocked polysiloxanes can be produced by equilibrating, among other reactants, monoalkyltrialkoxysilanes or dialkyldialkoxysilanes with cyclic polysiloxanes in the presence of a basic catalyst.
U.S. Pat. No. 3,024,126 (Brown, issued Mar. 6, 1962) teaches that reinforcing silica fillers can be surface-treated with certain hydroxy or alkoxy functional organosilanes in an organic solvent in the presence of certain basic catalysts. The Brown Patent teaches the use of certain lower molecular weight monoalkoxy- and dialkoxy-endblocked dihydrocarbonsiloxanes as surface treating agents, but teaches that there should not be more than three and preferably no more than one aliphatic, monovalent hydrocarbon radical per siloxane unit. If more than about three di-aliphatic-monovalent-hydrocarbon-radical-substituted silicon atoms in any siloxane molecule, the Brown Patent teaches that the effectiveness of the resulting treated silica will be substantially reduced.
U.S. Pat. No. 3,979,546 (Lewis, issued Sept. 7, 1976) teaches the surfaces of inorganic materials can be rendered hydrophobic by contacting them with alpha-alkoxy-omegasiloxanols containing one alkoxy group per molecule which are obtained from the reaction of cyclic siloxanes which alcohols under mild reaction conditions. While reasonably rapid conversion to product is obtained from hexamethylcyclotrisiloxane, Examples 3 and 4 indicate that conversion of octamethylcyclotetrasiloxane and decamethylcyclopentasiloxane to the corresponding alpha-alkoxy, omega-siloxanol useful as a treating agent was rather slow.
U.S. Pat. No. 2,927,909 (Lyons, et al., issued Mar. 8, 1960) teaches the use of (A) 65-85 parts by weight of a copolymer of 65-85 mole percent of monomethylsiloxane, 15-30 mole percent of dimethylsiloxane and no more than 5 mole percent of trimethylsiloxane which has from 1-12 weight percent silicon-bonded methoxy radicals and (B) from 15-35 parts by weight of monopropylsiloxane containing from 15 to 60% by weight silicon-bonded ethoxy radicals as a masonry water repellent. Nothing is taught concerning the use of component (A) and/or (B) to surface treat inorganic particulate fillers.
U.S. Pat. No. 2,706,724 (Bass, issued Apr. 19, 1955) teaches the use of a partial hydrolyzate of an alkoxylated (20-50 weight percent alkoxy radicals) mixture of by-product chlorosilicon compounds obtained from the reaction of CH.sub.3 Cl and Si as a water repellent treatment for masonry. Nothing is taught concerning the use of the compositions described in the Bass Patent for surface-treating inorganic particulate fillers.